Let me add a couple of worlds/settings to the list, if I may.
These come from past ideas of mine.
Manga (Dragon Ball, Gundam Wing, Macross...)
Star Wars
Middle Earth
Transformers (G1)
World of Darkness (original setting)
Wheel of Time
Song of Ice and Fire
Modern realistic (no magic)
Alien (the movie series)
I would happily play designs from any of the above (from both posts) and give feedback, etc. as a beta tester.
What am I really interested in working on, though? I guess it depends on my mood.
I guess it's just easier to say what I'm not interested in working on- Dragonlance (fond memories of the first trilogy, but didn't care for the magic system), Greyhawk (not familiar), Blackmoor (not familiar), Manga (burnt-out), Song of Ice and Fire (too hard to depict parallel stories), Alien (to hack n' slash).
What has stopped me from progressing on the other settings? Mostly, it has been the limitations of DC. Sometimes it's just a very small feature, sometimes it's a big one. Sometimes, it's just b/c I get overwhelmed.
Okay, I've thought about it a bit more, and at this moment, I would most be interested in working with Forgotten Realms, Star Wars, Marvel or Wheel of Time (in pretty much that order). This might chnage later today after I try out a couple of the Star Wars games I got for X-mas.